scholarly journals Numerical Analysis on Natural Convection Heat Transfer in a Single Circular Fin-Tube Heat Exchanger (Part 1): Numerical Method

Entropy ◽  
2020 ◽  
Vol 22 (3) ◽  
pp. 363 ◽  
Author(s):  
Jong Hwi Lee ◽  
Jong-Hyeon Shin ◽  
Se-Myong Chang ◽  
Taegee Min
Keyword(s):  
Natural Convection ◽  
Heat Exchanger ◽  
Rayleigh Number ◽  
Numerical Method ◽  
Stokes Equations ◽  
Convection Heat Transfer ◽  
Boussinesq Approximation ◽  
Tube Heat Exchanger ◽  
Fin Tube ◽  
Rayleigh Numbers

In this research, unsteady three-dimensional incompressible Navier–Stokes equations are solved to simulate experiments with the Boussinesq approximation and validate the proposed numerical model for the design of a circular fin-tube heat exchanger. Unsteady time marching is proposed for a time sweeping analysis of various Rayleigh numbers. The accuracy of the natural convection data of a single horizontal circular tube with the proposed numerical method can be guaranteed when the Rayleigh number based on the tube diameter exceeds 400, which is regarded as the limitation of numerical errors due to instability. Moreover, the effective limit for a circular fin-tube heat exchanger is reached when the Rayleigh number based on the fin gap size ( Ra s ) is equal to or exceeds 100. This is because at low Rayleigh numbers, the air gap between the fins is isolated and rarely affected by natural convection of the outer air, where the fluid provides heat resistance. Thus, the fin acts favorably when Ra s exceeds 100.

scholarly journals Numerical Analysis on Natural Convection Heat Transfer in a Single Circular Fin-Tube Heat Exchanger (Part 2): Correlations for Limiting Cases

Entropy ◽  
2020 ◽  
Vol 22 (3) ◽  
pp. 358 ◽  
Author(s):  
Jong Hwi Lee ◽  
Young Woo Son ◽  
Se-Myong Chang
Keyword(s):  
Natural Convection ◽  
Heat Exchanger ◽  
Circular Tube ◽  
Convection Heat Transfer ◽  
Type B ◽  
Flat Plates ◽  
Tube Heat Exchanger ◽  
Complex Correlation ◽  
C And N ◽  
Fin Tube

This research focused on the correlations associated with the physics of natural convection in circular fin-tube models. The limiting conditions are defined by two conditions. The lower limit ( D o / D → 1, s/D = finite value) corresponds to a horizontal circular tube, while the upper limit ( D o / D → ∞, s/D << 1) corresponds to vertical flat plates. In this paper, we proposed a corrected correlation based on empirical result. The circular fin-tube heat exchanger was divided into the A and B types, the categorizing criteria being D o / D = 1.2 , where D and D o refer to the diameter of the circular tube and the diameter of the circular fin, respectively. Moreover, with the computational fluid dynamics technique used to investigate the limiting conditions, the parametric range was extended substantially in this research for type B, namely 1.2 < D o / D ≤ 10. The complex correlation was also simplified to the form Nu L = C Ra s n , where C and n are the functions of the diameter ratio D o / D .

A Numerical Study of Natural Convection in a Cavity With Two Fins Attached to Its Vertical Walls

2007 ◽  
Author(s):  
G. A. Sheikhzadeh ◽  
M. Pirmohammadi ◽  
M. Ghassemi
Keyword(s):  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Square Cavity ◽  
Vertical Walls ◽  
The Mean ◽  
Energy Equations ◽  
Rayleigh Numbers

Numerical study natural convection heat transfer inside a differentially heated square cavity with adiabatic horizontal walls and vertical isothermal walls is investigated. Two perfectly conductive thin fins are attached to the isothermal walls. To solve the governing differential mass, momentum and energy equations a finite volume code based on Pantenkar’s simpler method is developed and utilized. The results are presented in form of streamlines, isotherms as well as Nusselt number for Rayleigh number ranging from 104 up to 107. It is shown that the mean Nusselt number is affected by the position of the fins and length of the fins as well as the Rayleigh number. It is also observed that maximum Nusselt number occurs about the middle of the enclosure where Lf is grater the 0.5. In addition the Nusselt number stays constant and does not varies with width of the cavity (lf) when Lf is equal to 0.5 and Rayleigh number is equal to 104 and 107 as well as when Lf is equal to 0.6 and low Rayleigh numbers.

Natural Convection Heat Transfer in a Rectangular Water Pool with Internal Heating and Top and Bottom Cooling

2006 ◽  
Author(s):  
Jong K. Lee ◽  
Seung D. Lee ◽  
Kune Y. Suh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Rayleigh Number ◽  
Test Section ◽  
Convection Heat Transfer ◽  
The Other ◽  
Natural Convection Heat Transfer ◽  
Convection Heat

During a severe accident, the reactor core may melt and be relocated to the lower plenum to form a hemispherical pool. If there is no effective cooling mechanism, the core debris may heat up and the molten pool run into natural convection. Natural convection heat transfer was examined in SIGMA RP (Simulant Internal Gravitated Material Apparatus Rectangular Pool). The SIGMA RP apparatus comprises a rectangular test section, heat exchanger, cartridge heaters, cooling jackets, thermocouples and a data acquisition system. The internal heater heating method was used to simulate uniform heat source which is related to the modified Rayleigh number Ra′. The test procedure started with water, the working fluid, filling in the test section. There were two boundary conditions: one dealt with both walls being cooled isothermally, while the other had to with only the upper wall being cooled isothermally. The heat exchanger was utilized to maintain the isothermal boundary condition. Four side walls were surrounded by the insulating material to minimize heat loss. Tests were carried out at 1011 &lt; Ra′ &lt; 1013. The SIGMA RP tests with an appropriate cartridge heater arrangement showed excellent uniform heat generation in the pool. The steady state was defined such that the temperature fluctuation stayed within ±0.2 K over a time period of 5,000 s. The conductive heat transfer was dominant below the critical Rayleigh number Ra′c, whereas the convective heat transfer picked up above Ra′c. In the top and bottom boundary cooling condition, the upward Nusselt number Nuup was greater than the downward Nusselt number Nudn. In particular, the discrepancy between Nuup and Nudn widened with Ra′. The Nuup to Nudn ratio was varied from 7.75 to 16.77 given 1.45×1012 &lt; Ra′ &lt; 9.59×1013. On the other hand, Nuup was increased in absence of downward heat transfer for the case of top cooling. The current rectangular pool testing will be extended to include circular and spherical pools.

Study on the Route to Chaos of Natural Convection in Cylindrical Envelope With an Internal Concentric Cylinder With Slots

2010 ◽  
Author(s):  
Kun Zhang ◽  
Mo Yang ◽  
Yu Wen Zhang ◽  
Mei Lu
Keyword(s):  
Steady State ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
Period Doubling ◽  
Simple Algorithm ◽  
Concentric Cylinder ◽  
Initial Field ◽  
Volume Method ◽  
Rayleigh Numbers

Natural convection heat transfer was investigated numerically in a cylindrical envelope with an internal concentric cylinder with slots. Governing equations are discretized using finite volume method and solved using SIMPLE algorithm with QUICK scheme. Calculations were performed on certain parameters with a Rayleigh number varying from 700 to 20000. The effect of the Rayleigh number on the route to the chaos of the system was analyzed by the phase space of velocity at the sample point. The results show that the system can reach to steady state and symmetric when the Rayleigh number is below 700, and to steady state and asymmetric when the Rayleigh number is equal to 1000. For a Rayleigh number ranged between 1500 and 3000, an asymmetric periodical solution is obtained although the initial field and boundary conditions were symmetric. As the Rayleigh numbers increase further, a quasi-periodic solution of the system is achieved at Ra = 2000. There is one more bifurcation and period doubling at successive critical values of Rayleigh numbers from to. It is ascertained that periodicity is lost at Ra = 20000. The results show that the oscillatory flow undergoes several bifurcations and ultimately evolves to a chaotic flow.

Natural Convection Correlations of Circular Finned Tube Heat Exchanger

2011 ◽  
Author(s):  
Hie Chan Kang ◽  
Hyun Soon Jang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Convection Heat Transfer ◽  
Small Diameter ◽  
Finned Tube ◽  
Tube Heat Exchanger ◽  
Finned Tube Heat Exchanger ◽  
Half Power

An experimental study has been conducted on natural convection heat transfer for seventeen kinds of circular finned tube heat exchanger. The transient method was used to obtain the heat transfer coefficient. The experimental data were presented and their characteristics lengths were discussed. The experimental data were presented and correlated in the ranges of 27 < RaDh < 2300, 1.2 < Do/Di < 2.8, and 0.12 < Pf/Di < 0.26. The Nusselt number correlated with the quarter power of the Rayleigh number, based on the hydraulic diameter, for the small diameter fins, the same as laminar natural convection; however, the correlation was with the half power for the large fin diameters and small fin pitches.

scholarly journals Experimental investigation of natural convection in an enclosure with partial partitions at different angles

2014 ◽  
Vol 18 (4) ◽  
pp. 1133-1144 ◽  
Author(s):  
Osameh Ghazian ◽  
Hossein Rezvantalab ◽  
Mehdi Ashjaee
Keyword(s):  
Natural Convection ◽  
Rayleigh Number ◽  
Wood Fiber ◽  
Convection Heat Transfer ◽  
Heated Wall ◽  
Isolated Cells ◽  
Nusselt Numbers ◽  
Vertical Walls ◽  
Rayleigh Numbers ◽  
Partial Partitions

Natural convection heat transfer in a partially partitioned enclosure has been investigated experimentally using Mach-Zehnder Interferometry technique. The top and bottom of the enclosure are insulated while one of the vertical walls is heated isothermally. The partitions are made of wood fiber and are attached to the heated wall with angles changing from 30? to 150? in different experiments. The length of each partition is equal to the width of the enclosure, therefore dividing the enclosure to isolated cells only at 90?. At other angles the cells are interconnected near the cold wall. Rayleigh number based on the enclosure width is changed from 3500 to 32000. Results for the local and the average Nusselt numbers at the heated wall of the enclosure are presented and discussed for various partition angles and Rayleigh numbers. It is found that, at each Rayleigh number, there exists an optimum inclination angle which minimizes the average Nusselt number.

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